Link switch in a wireless communication system

ABSTRACT

A wireless communication device is configured for use in a wireless communication system. The device in this regard is configured to receive a command that commands the device to perform a link switch from a source link to a target link responsive to fulfillment of a condition. The command may indicate a target link configuration relative to a source link configuration. The device is also configured to store information from which the target link configuration indicated by the command is determinable irrespective of any change to the source link configuration occurring after receipt of the command. In some embodiments, the device is configured to, responsive to fulfillment of the condition, perform a link switch from the source link to the target link using the target link configuration as determined from the stored information.

RELATED APPLICATIONS

This application is a continuation of prior U.S. application Ser. No.16/319,375, filed 21 Jan. 2019, which was the National Stage ofInternational Application PCT/SE2017/051326 filed 21 Dec. 2017, whichclaims the benefit of U.S. Provisional Application No. 62/446,822, filed16 Jan. 2017, the entire disclosure of each being hereby incorporated byreference herein.

TECHNICAL FIELD

The present application relates generally to a wireless communicationsystem, and relates specifically to link switch in a wirelesscommunication system.

BACKGROUND

As channel conditions for a wireless communication device change, thedevice may switch (e.g., handover or reselect) from one wireless link toanother in order to maintain service continuity. The device may forexample switch from accessing the system via one access node, cell,sector, or beam (any of which may serve as a “link”) to accessing thesystem via a different access node, cell, sector, or beam. Towards thisend, when channel conditions on the link via which the device currentlyaccesses the system deteriorates, the system may evaluate which ofdifferent candidate target links the device should switch to, if any.The device in this regard may perform measurements on the differentcandidate target links and report those measurements to another node inthe network (e.g., the serving access node), so that the other node canmake the link switch decision. Once the link switch decision is made,the node may command the device to switch to a chosen target link.

Known link switch approaches are susceptible to high latency that provesespecially problematic when a link switch must be performed quickly,e.g., before the serving link's quality degrades excessively. However,reducing link switch latency while at the same time maintainingefficient signalling schemes proves challenging.

SUMMARY

According to one or more embodiments herein, a network node sends acommand to a wireless communication device to switch from a source linkto a target link responsive to fulfilment of a condition (e.g., asdetected by the device). With the link switch conditionally commanded inthis way, the command may be sent to the device earlier in time ascompared to traditional approaches, so as to improve link switchrobustness to degrading source link quality. Furthermore, someembodiments herein efficiently signal the target link configurationrelative to the source link configuration, yet still ensure that thesignalled target link configuration is recoverable or otherwisedeterminable even if the source link configuration changes (e.g., in theinterim between when the link switch is conditionally commanded and whenthe link switch is performed).

More particularly, embodiments herein include a method performed by awireless communication device configured for use in a wirelesscommunication system. The method may comprise receiving a command thatcommands the wireless communication device to perform a link switch froma source link to a target link responsive to fulfillment of a condition.The command may indicate a target link configuration relative to asource link configuration. The method may also comprise storinginformation from which the target link configuration indicated by thecommand is determinable irrespective of any change to the source linkconfiguration occurring after receipt of the command. In someembodiments, the method may further comprise performing one or moreoperations based on the stored information. In one example, forinstance, performing one or more operations based on the storedinformation may comprise, responsive to fulfillment of the condition,performing a link switch from the source link to the target link usingthe target link configuration as determined from the stored information.

In some embodiments, the command includes relative reconfigurationinformation that indicates the target link configuration relative to thesource link configuration. The relative reconfiguration information mayfor instance include one or more parameter values that are differentbetween the target link configuration and the source link configuration,and exclude one or more parameter values that are the same between thetarget link configuration and the source link configuration. Regardless,the information from which the target link configuration indicated bythe command is determinable may comprise the relative reconfigurationinformation and/or the source link configuration as of when the commandis received.

In some embodiments, the method may further comprise, responsive tofulfillment of the condition, determining the target link configurationfrom the stored information. That is, determination of the target linkconfiguration may be deferred until fulfillment of the condition for thelink switch. In other embodiments, by contrast, the target linkconfiguration indicated by the command may be determined responsive toreceiving the command or responsive to determining that the source linkconfiguration is to be changed. In these and other embodiments, then,the method may comprise storing the determined target link configurationas the stored information.

In any of these embodiments, the method may comprise, after storing theinformation from which the target link configuration indicated by thecommand is determinable, changing the source link configuration andpreserving the stored information irrespective of the change to thesource link configuration.

In some embodiments, the method may comprise associating the storedinformation with the condition, receiving an update to the condition,and updating the condition in accordance with the received update whilepreserving the stored information and the association of the conditionwith the stored information. Alternatively or additionally, the methodmay comprise associating the stored information with a validity timerfor the command, receiving an update to the validity timer, and updatingthe validity timer in accordance with the received update whilepreserving the stored information and the association of the validitytimer with the stored information.

In any of the embodiments, the target link configuration may specify arandom access configuration for randomly accessing the target link.

In some embodiments, the condition is fulfilled when a signalmeasurement for the target link exceeds a signal measurement for thesource link by at least a defined amount.

In some embodiments, the target link configuration is a radio resourcecontrol, RRC, configuration for the target link.

In some embodiments, the condition is a measurement configurationassociated with a measurement event. For example, in some embodiments,the measurement configuration is provided explicitly in said conditionalswitch command. Alternatively or additionally, the measurementconfiguration is part of said source link configuration and wherein saidconditional switch command comprises a reference to said measurementconfiguration.

Embodiments further include corresponding apparatus, computer programs,and computer readable medium.

Embodiments for instance include a wireless communication deviceconfigured for use in a wireless communication system. The wirelesscommunication device in this regard is configured to receive a commandthat commands the wireless communication device to perform a link switchfrom a source link to a target link responsive to fulfillment of acondition. The command may indicate a target link configuration relativeto a source link configuration. The wireless communication device isalso configured to store information from which the target linkconfiguration indicated by the command is determinable irrespective ofany change to the source link configuration occurring after receipt ofthe command. In some embodiments, the wireless communication device isalso configured to perform one or more operations based on the storedinformation. In one example, for instance, the wireless communicationdevice is configured to, responsive to fulfillment of the condition,perform a link switch from the source link to the target link using thetarget link configuration as determined from the stored information.

Embodiments further include a method performed by a network nodeconfigured for use in a wireless communication system. The methodcomprises transmitting a command that commands a wireless communicationdevice to perform a link switch from a source link to a target linkresponsive to fulfillment of a condition, wherein the command indicatesa target link configuration relative to a source link configuration. Themethod may also comprise, after transmitting the command, changing thesource link configuration. The method may further comprise, afterchanging the source link configuration, transmitting an updated commandthat indicates an updated target link configuration relative to thesource link configuration before the source link configuration waschanged.

In some embodiments, the method further comprises signaling that theupdated command indicates the updated target link configuration relativeto the source link configuration before the source link configurationwas changed.

In some embodiments, the command includes relative reconfigurationinformation that indicates the target link configuration relative to thesource link configuration as of when the command is transmitted.

In some embodiments, the relative reconfiguration information includesone or more parameter values that are different between the target linkconfiguration and the source link configuration as of when the commandis transmitted, and excludes one or more parameter values that are thesame between the target link configuration and the source linkconfiguration as of when the command is transmitted.

In some embodiments, the target link configuration specifies a randomaccess configuration for randomly accessing the target link.

In some embodiments, the condition is fulfilled when a signalmeasurement for the target link exceeds a signal measurement for thesource link by at least a defined amount.

In some embodiments, the target link configuration is a radio resourcecontrol, RRC, configuration for the target link.

Embodiments further include corresponding apparatus, computer programs,and computer readable medium.

For example, embodiments include a network node configured for use in awireless communication system. The network node is configured totransmit a command that commands a wireless communication device toperform a link switch from a source link to a target link responsive tofulfillment of a condition, wherein the command indicates a target linkconfiguration relative to a source link configuration. The network nodeis also configured to, after transmitting the command, change the sourcelink configuration. The network node is further configured to, afterchanging the source link configuration, transmit an updated command thatindicates an updated target link configuration relative to the sourcelink configuration before the source link configuration was changed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a wireless communication system thatincludes a wireless device and a network node according to someembodiments.

FIG. 2 is a logic flow diagram of a method performed by a wirelessdevice according to some embodiments.

FIG. 3 is a call signaling diagram of a procedure for a conditional linkswitch according to some embodiments.

FIG. 4 is a call signaling diagram of a procedure for a conditional linkswitch according to other embodiments.

FIG. 5A is a block diagram of a wireless device according to someembodiments.

FIG. 5B is a block diagram of a wireless device according to otherembodiments.

FIG. 6 is a logic flow diagram of a method performed by a network nodeaccording to some embodiments.

FIG. 7A is a block diagram of a network node according to someembodiments.

FIG. 7B is a block diagram of a network node according to otherembodiments.

DETAILED DESCRIPTION

FIG. 1 illustrates a wireless communication system 10 according to oneor more embodiments. As shown, the system 10 (e.g., a 5G system) mayinclude an access network (AN) 12 and a core network (CN) 14. The AN 12wirelessly connects a wireless communication device 16 (or simply“wireless device 16”) to the CN 14. The CN 14 in turn connects thewireless device 16 to one or more external networks (not shown), such asa public switched telephone network and/or a packet data network (e.g.,the Internet).

The AN 12 provides links via which the wireless device 16 may wirelesslyaccess the system 10, e.g., using uplink and/or downlink communications.The AN 12 may for example provide links in the form of access nodes(e.g., base stations), cells, sectors, beams, or the like. Some linksmay provide wireless coverage over different geographical areas.

A network node 18 controls which link the device 16 uses to access thesystem 10. The network node 18 may be in the AN 12 (e.g., in the form ofa base station), or may be in the CN 14 (e.g., in the form of a mobilitymanagement entity, MME, or access and mobility function, AMF). Thenetwork node 18 may control which link the device 16 uses by for exampledeciding that the device 16 is to switch (e.g., handover or reselect)from accessing the system 10 via one link (the “source” link) toaccessing the system 10 via another link (the “target” link). Thenetwork node 18 may choose the target link from among a set of multiplelinks that the network node 18 considers as candidates for the targetlink.

However, rather than unconditionally commanding the device 16 to switchfrom the source link to a chosen target link, the network node 18 insome embodiments conditionally commands the device 16 to perform such alink switch. FIG. 1 in this regard shows that the wireless communicationdevice 16 may receive a conditional switch command 22, e.g., from or viathe network node 18. Where the link switch is a handover, for instance,the command 22 may be a conditional handover command. Regardless, theconditional switch command 22 as shown “conditionally” commands thedevice 16 to perform a link switch 24 from a source link 20A to a targetlink 20B. The device 16 in particular is to perform that link switch 24responsive to fulfilment of a condition (e.g., responsive to the device16 detecting that the target link's signal strength or quality exceedsthat of the source link by at least a defined amount). In someembodiments, for example, the device 16 may autonomously perform thelink switch 24 as soon as the device 16 itself detects fulfilment of thecondition. Conditionally performing the link switch 24 in this way mayfor instance improve the robustness of the link switch 24 againstdeteriorating source link conditions.

FIG. 1 also illustrates that in some embodiments the conditional switchcommand 22 indicates a target link configuration 26, e.g., to be used bythe device 16 for the target link 20B to which the command 22conditionally commands the device 16 to switch. The target linkconfiguration 26 may be for instance a radio resource control (RRC)configuration to be used for the target link 20B, e.g., provided via anRRCConnectionReconfiguration message in LTE embodiments or via anRRCReconfiguration message in New Radio (NR) embodiments. The targetlink configuration 26 may for instance contain configuration parametersfor data radio bearers, signalling radio bearers, medium access control(MAC), radio link control (RLC), packet data convergence protocol(PDCP), and/or physical layer used for the target link 20B.Configuration parameters may for example be for data and controlchannels, such as used for a random access channel. The target linkconfiguration 26 in this regard may specify a random accessconfiguration (e.g., in terms of a random access preamble or the like)that the device 16 is to use for connecting to the target link 20B. Therandom access configuration in this regard may include one or more setsof parameters that define when (in time), where (in frequency), and/orhow (e.g., in terms of codes/preambles, power, periodicity) the device16 may send random access requests for connecting to the target link20B.

Regardless of the particular type of configuration 26, the conditionalswitch command 22 may indicate the target link configuration 26 relativeto a source link configuration 28, e.g., the (e.g., RRC) configuration28 used by the device 16 for the source link 20B from which the command22 conditionally commands the device 16 to switch. The command 22 mayfor instance include (or otherwise be associated with) relative (or“delta”) reconfiguration information that defines the target linkconfiguration 26 relative to the source link configuration 28. Therelative reconfiguration information in some embodiments, for example,includes one or more parameter values that are different between thetarget link configuration 26 and the source link configuration 28, andexcludes one or more parameter values that are the same between thetarget link configuration 26 and the source link configuration 28. Thecommand 22 in this regard effectively assumes that the device 16 alreadyknows the parameter values of the target link configuration 26 which arethe same as those of the source link configuration 28 as of when thecommand 22 is received, and therefore efficiently refrains fromneedlessly signaling those parameter values to the device 16. The device16 in such case may be configured to form, derive, or otherwisedetermine the target link configuration 26 from the parameter valuesincluded in the command 22, in combination with any parameter valuesfrom the source link configuration 27 that are not included in thecommand 22.

Signalling the target link configuration 26 relative to the source linkconfiguration 28 in this way may prove efficient in some embodiments.However, unless properly accounted for, changes in the source linkconfiguration 28 may threaten to in turn change what target linkconfiguration the device 16 detects as being signalled. The command 22may for instance be built based on the source link configuration 28 asit (currently) exists at the time of command building, and changes tothe source link configuration 28 that occur after command building mayaffect what target link configuration the device 16 interprets as beingsignalled by the command 22. This proves especially the case since theswitch command 22 is conditional in nature. If, for example, the device16 waits until the condition for the link switch occurs before naivelydetermining the target link configuration 26 signalled, the device 16may determine a different target link configuration than that actuallysignalled if the source link configuration 28 has changed in theinterim.

To account for these and other problems surrounding configurationsignalling, the device 16 in some embodiments herein stores information30 from which the target link configuration 26 indicated by theconditional switch command 22 is determinable irrespective of any changeto the source link configuration 28 occurring after receipt of theconditional switch command 22. That is, the information 30 storedenables the device 16 to determine the target link configuration 26signalled, even if the source link configuration 28 changes after thedevice 16 receives the command 22. In some embodiments, for instance,the device 16 may memorialize or preserve the information 30 as stored(e.g., in memory), even if the source link configuration 28 is changed.With this information 30 preserved, the device 16 may be configured todetermine 32 the signalled target link configuration 26 from the storedinformation 30, e.g., as opposed to with reference to whatever thecurrent source link configuration 28 is, since that source linkconfiguration 28 may have changed since the command 22 was built.Accordingly, no matter whether the source link configuration 28 ischanged after receipt of the command 22, the device 16 may stilldetermine the target link configuration 26 that was indicated by thecommand 22.

In some embodiments, for example, the information 30 stored includes thesource link configuration 28 as of when the command 22 is received, orat least a portion thereof, e.g., as preserved or memorialized at thetime the conditional switch command 22 is received. The device 16 mayfor instance store the source link configuration 28 in full or in partresponsive to receiving the conditional switch command 22. Then, later(e.g., upon condition fulfilment), the device 16 may (retroactively)determine the target link configuration 26 that was indicated by theconditional switch command 22, by referencing the stored source linkconfiguration 28, rather than the current source link configurationwhich may have since changed.

Alternatively or additionally, the information 30 stored may include therelative reconfiguration information mentioned above. The information 30stored in such case may include the one or more parameters of the targetlink configuration 26 that are different from those of the source linkconfiguration 28 as of when the command is received. When the relativereconfiguration information is stored in conjunction with the sourcelink configuration 28, the stored information 30 thereby memorializes orpreserves the target link configuration 26 as it was signalled by thecommand 22 in “relative” form.

In other embodiments, by contrast, the device 16 may memorialize orpreserve the target link configuration 26 in “absolute” form, i.e., in aform that is not relative to the source link configuration 28. In someembodiments, for example, the device 16 determines the target linkconfiguration 26 indicated by the conditional switch command 22 andstores that determined target link configuration 26 as the storedinformation 30. In some sense, then, the information 30 stored is an“absolute” target link configuration 26 that does not rely on anyrelativity to the source link configuration 28, as opposed to the“relative” target link configuration 26 signalled in the command 22 asbeing relative to the source link configuration 28.

In any event, the device 16 may determine the target link configuration26 for storing in “absolute” form at any time after receiving thecommand 22 and before the source link configuration 28 is changed. Inone embodiment, for example, the device 16 is configured to determinethe target link configuration 26 indicated by the conditional switchcommand 22 responsive to (e.g., upon) receiving that command 22. Thisway, the source link configuration 28 will not have changed,guaranteeing that the determined target link configuration 26 representsthe configuration intended to be signalled. In other embodiments, bycontrast, the device 16 may wait to determine the target linkconfiguration 26 until the source link configuration 28 is about to bechanged. The device 16 may for instance determine the target linkconfiguration 26 indicated by the conditional switch command 22responsive to receiving a reconfiguration message indicating that thesource link configuration 28 is to be changed. In either approach,though, the device 16 stores the determined target link configuration26, so as to memorialize that configuration 26 for a potential linkswitch 24 upon fulfillment of the associated condition.

Memorialization of the signaled target link configuration 26 using thestored information may mean that the device 16 preserves that storedinformation 30 even if the source link configuration 28 changes. Thatis, the device 16 in some embodiments may change the source linkconfiguration 28 (e.g., as directed by the network node 18) afterstoring the information 30, but may preserve that stored information 30irrespective of such change to the source link configuration 28.

Similarly, the device 16 may preserve the stored information 30 even ifthe network node 18 signals an update to command 22, e.g., to change thecondition for performing the link switch 24 and/or to change a validitytimer for the command 22. In some embodiments, for instance, the device16 may associate the stored information 30 with the condition forperforming the link switch 24. In this case, when the device 16 receivesan update to the condition, the device 16 may update the condition inaccordance with the received update while preserving the storedinformation 30 and the association of that stored information 30 withthe (now updated) condition. Alternatively or additionally, the device16 may associate the stored information 30 with a validity timer for thecommand 22, e.g., that indicates a duration for how long the command 22remains valid. In this case, when the device 16 receives an update tothe validity timer (e.g., extending the time for which the command 22 isvalid), the device 16 may update the validity timer in accordance withthe received update while preserving the stored information 30 and theassociation of that stored information 30 with the (now updated)validity timer.

Under some conditions, though, such as when the stored information is nolonger needed, the stored information 30 may be discarded or replaced.For example, under some circumstances, the link switch 24 to the targetlink 20B may be canceled prior to the fulfilment of the condition. Insome embodiments, for instance, the device 16 may cancel the link switch24 responsive to receiving a command to specifically cancel the linkswitch 24, or to generally cancel any link switch for which a respectivecondition has not been fulfilled. In other embodiments, the device 16may cancel the link switch 24 responsive to receiving a command toperform a link switch from the source link 20A to a different targetlink, or responsive to successfully performing (or signalingconfirmation of) a link switch from the source link 20A to a differenttarget link. Regardless, responsive to canceling the link switch 24, thedevice 16 may discard the stored information 30, e.g., as no longerbeing needed since the target link configuration 26 no longer needs tobe determined. In some embodiments, however, the device 16 may onlydiscard the stored information 30 if the device 16 indeed determinesthat the stored information 30 is not needed, e.g., as opposed toassuming that such is the case simply upon cancelling the link switch24.

Indeed, in these and other embodiments, the device 16 may receive one ormore conditional switch commands 22 that command the device 16 toperform a link switch from the source link 20A to different target linksresponsive to fulfillment of respective conditions. For the respectivetarget links, the one or more commands may indicate respective targetlink configurations, which may be the same or different across thetarget links. The device 16 may thereby store information from which therespective target link configurations are each determinable. Forexample, where the respective target link configurations are indicatedrelative to the same source link configuration 28, the device 16 in someembodiments may store the source link configuration 28 from which therespective target link configurations may be determinable (e.g., inconjunction with relative reconfiguration information associatedrespectively with the individual target links). Accordingly, withmultiple target link configurations determinable from the same storedsource link configuration 28, the device 16 may only discard that storedinformation upon determining that no target link configuration isdeterminable from the stored source link configuration 28. For example,if a link switch to one of the target links is canceled, but at leastone other link switch to another of the target links remains pending,the device 16 may continue to preserve the stored information, at leastto the extent needed to determine the target link configuration for thepending link switch.

Under some conditions, the device 16 in other embodiments may simplyupdate the stored information rather than discarding it. For example,the device 16 may receive an updated command for the target link thatindicates an updated target link configuration relative to the samesource link configuration. In this case, the device 16 may replace thestored information 30 with information from which the updated targetlink configuration is determinable irrespective of any changes to thesource link configuration occurring after receipt of the updatedcommand.

In view of the above modifications and variations, FIG. 2 generallyillustrates processing performed by the wireless communication device 16according to some embodiments. As shown, the processing may includereceiving a command 22 that commands the wireless communication device16 to perform a link switch 24 from a source link 20A to a target link20B responsive to fulfillment of a condition (Block 100). The command 22may indicate a target link configuration 26 relative to a source linkconfiguration 28. Processing as shown in FIG. 2 may also include storinginformation 30 from which the target link configuration 26 indicated bythe command 22 is determinable irrespective of any change to the sourcelink configuration 28 occurring after receipt of the command 22 (Block110).

In some embodiments, processing may also include performing one or moreoperations based on the stored information 30 (Block 120). In oneembodiment, for example, performing one or more operations based on thestored information 30 may comprise, responsive to fulfillment of thecondition, performing a link switch 24 from the source link 20A to thetarget link 20B using the target link configuration 26 as determinedfrom the stored information 30.

In other embodiments, these one or more operations may relate tomanaging the stored information 30. For example, the device 16 may beconfigured to discard or delete the stored information 30 if it is nolonger applicable to a pending link switch, e.g., if the conditionallink switch is canceled prior to the associated condition beingfulfilled. In some embodiments, for instance, the one or more operationscomprise canceling the link switch to the target link prior tofulfillment of the condition, and discarding the stored informationresponsive to such canceling. Cancelation of a conditional link switchmay occur for instance responsive to receipt of a cancel switch command,receiving a switch command that commands a switch to a different targetlink, and/or successfully performing, or signaling confirmation of, aswitch to a different link.

One or more additional embodiments will now be described in a contextwhere the system 10 is a 5G or New Radio (NR) system, a link is a cell,the link switch 24 is a handover, and the link configuration is an RRCconfiguration.

In more detail, one of the main goals of New Radio (NR) is to providemore capacity for operators to serve ever increasing traffic demands anda variety of applications. Because of this, NR will be able to operateon high frequencies like frequencies over 6 GHz up to 60 or even 100GHz. In comparison to the current frequency bands allocated to Long TermEvolution (LTE), some of the new bands will have much more challengingpropagation properties such as lower diffraction and higheroutdoor/indoor penetration losses. As a consequence, signals will haveless ability to propagate around corners and penetrate walls. Inaddition, in high frequency bands, atmospheric/rain attenuation andhigher body losses render the coverage of NR signals even more spotty.

Fortunately, the operation in higher frequencies makes it possible touse smaller antenna elements, which enables antenna arrays with manyantenna elements. Such antenna arrays facilitate beamforming, wheremultiple antenna elements are used to form narrow beams and therebycompensate for the challenging propagation properties.

Despite the link budget gains provided by beamforming solutions,reliability of a system purely relying on beamforming and operating inhigher frequencies might be challenging, since the coverage might bemore sensitive to both time and space variations. As a consequence ofthat, the signal-to-interference-plus-noise ratio (SINR) of such anarrow link can drop much quicker than in the case of LTE. The servingcell may therefore not be able to convey a handover command timely.Lowering the Time-To-Trigger (TTT) parameter and the measurementhysteresis reduces the handover failure rate, but also results in higherping-pong probability. Accordingly, quickly degrading link qualityprohibits delivery of the handover (HO) command from the source cell tothe user equipment (UE), which leads ultimately to a handover failure.In NR, these effects will be even more pronounced when operating athigher frequency bands. To ensure that NR offers at least as robustmobility (as low or lower Handover-Failure (HOF) rates) as LTE, there isa need to put attention to mobility robustness in NR systems.

In LTE and NR, different solutions to increase mobility robustness havebeen discussed. One area of solutions is based on Dual Connectivityintroduced in LTE Rel-12. In Dual Connectivity, the UE is connected totwo network nodes at the same time. This allows improving mobilityrobustness by serving control plane traffic (e.g. used for measurementreporting and handover command) by the more robust macro layer on lowfrequency and providing a capacity boost by higher layers. This featureis called user Plane (UP)/Control Plane (CP) split. One variant of DualConnectivity is RRC diversity feature, which allows sending controlplane signaling over two nodes. This increases diversity in temporal andspatial domain and thus increases robustness.

One issue of Dual Connectivity solutions is that the UE must be servedwith two connections. This can become problematic as network resourcesare consumed more. In addition, Dual Connectivity requires two differentreceive/transmit (RX/TX) chains in the UE side which comes with thedevice manufacturing cost. Because of that, also alternative solutionsshould be considered.

In order to avoid the undesired dependence on the serving radio linkupon the time (and radio conditions) where the UE should execute thehandover, NR according to some embodiments may provide RRC signaling forthe handover to the UE earlier than conventional. To achieve this, thehandover command may be associated with a condition. As soon as thecondition is fulfilled, the UE may execute the handover in accordancewith the provided handover command.

Such a condition may e.g. be based on the comparison of measurementresults that the UE acquires, also known as “measurement event”. Anevent or condition is typically expressed as an equation and consideredto be fulfilled if the equation is “true”. An example for a measurementevent is an equation that compares a measurement quantity (typically“signal strength” or “signal quality”) determined for a neighbor cell(e.g. “rsrpNeighbour”) with the measurement quantity determined for theserving cell (e.g. “rsrpServing”). Besides these two measurement values,there may be an additional threshold or hysteresis (e.g. thresholdX).The event is then considered fulfilled, if“rsrpNeighbour>rsrpServing+thresholdX”. Hence, the UE would in thisexample execute the handover when the signal strength (RSRP) of theneighbor cell becomes more than X (dB) better than the signal strengthof the serving cell.

The handover procedure (negotiation between source cell and candidatetarget cell and provisioning of a handover command via the source cellto the UE) may be triggered by a measurement report. The serving cellconfigures the UE with measurement events (conditions) that areassociated with measurement configurations. If such a measurement eventis fulfilled, the UE generates a measurement report comprisingmeasurement quantities (e.g. signal strength) for one or more detectedcells (serving and/or neighbor cells). The UE then sends the measurementreport to its serving cell so that the serving cell can decide whetheror not to initiate said handover procedure towards any of the reportedneighbor cells. The measurement event triggering the measurement reportmay use the same condition (e.g., formula) as mentioned above. However,a thresholdY in the condition for the measurement report triggering maybe chosen lower than the thresholdX in the handover execution condition.This allows the serving cell to prepare the handover upon reception ofan early measurement report and to provide anRRCConnectionReconfiguration with mobilityControlInfo at a time when theradio link between the source cell and the UE is still stable (neighboris only Y dB better than serving, where Y may e.g. be set to 0). Theexecution of the handover is done at a later point in time (when theneighbor is already X dB better than serving, where X may e.g. be 3 dB)when the radio conditions are considered optimal for the handoverexecution.

FIG. 3 depicts an example with a serving cell and just one target cell.As shown, a UE 40 receives user plane (UP) data from a serving cell 50(step 0). Upon fulfillment of a measurement event (e.g., based on a low′threshold such as a thresholdY), the UE 40 sends a measurement report tothe serving cell 50 (Step 1). The measurement report may include ameasurement quantity for a target cell 60. Based on the report, theserving cell 50 in this example makes a decision to prepare the targetcell 60 for a potential handover (Step 1A). Based on this decision,then, the serving cell 50 sends a handover request to the target cell 60(Step 2), which may happen earlier than in a conventional handoverprocedure given the low threshold for the measurement report. Where thehandover request is sent early in this way, it may be referred to as an“early HO request” as shown in FIG. 3 . The target cell 60 accepts thehandover in response to the request, and builds an RRC configuration forthe UE 40 to use with the target cell 60 (Step 2A). The target cell 60then sends a handover acknowledgement to the serving cell 50 includingthe built RRC configuration (Step 3). The serving cell 50correspondingly sends a conditional handover command to the UE 40 thatcommands the UE 40 to handover to the target cell 60 responsive tofulfillment of a condition (Step 4). This condition may be based on a‘high’ threshold (E.g., thresholdX) that is higher than the lowthreshold which triggered the measurement report. When measurement ofthe target cell 60 fulfills the handover condition (e.g., based on thehigh threshold), the UE 40 autonomously triggers the pending conditionalhandover to the target cell 60 (Step 4A). The UE 40 in this regardperforms synchronization and random access with the target cell 60 (Step5) and confirms handover to the target cell 60 (Step 6). After signalingthe completion of the handover to the serving cell 50 (Step 7), thetarget cell 60 may provide user plane data to the UE (Step 8).

In practice, though, there may often be many cells or beams that the UEreports as possible candidates based on its preceding radio resourcemanagement (RRM) measurements. The network may then have the freedom toissue conditional handover commands for several of those candidates. TheRRCConnectionReconfiguration for each of those candidates may differe.g. in terms of the HO execution condition (reference signal to measureand threshold to exceed) as well as in terms of the random accesspreamble to be sent when a condition is met.

The RRCConnectionReconfiguration may be a “delta” to the UE's currentconfiguration, i.e., the RRCConnectionReconfiguration message does notcomprise all parameters that determine the UE configuration but only theones that have changed compared to the UEs current configuration. Insome embodiments, the UE shall apply RRCConnectionReconfigurationmessages in the order in which it receives them, which is, due to theproperties of the Radio Link Control (RLC) protocol, as well as theorder in which the network generated and sent them.

The UE may be able to determine unambiguously how to apply the (delta)configuration provided in the conditional handover command so that theconfiguration used thereafter by the UE is in-line with what the networkexpects. In some embodiments, therefore, the triggering conditionassociated with the HO command sent to the UE should evaluatemeasurements and trigger the handover when those conditions arefulfilled. But since the HO command configuration may be a delta to theUE's current RRC configuration, one or more embodiments address how tohandle subsequent RRCConnectionReconfiguration messages arriving fromthe source cell if the UE has not yet executed the handover.

When the UE receives a “conditional HO command” it may interpret theRRCConnectionReconfiguration with mobilityControlInfo as a delta to itscurrent configuration (unless it is a full configuration message). Itmay in principle determine the resulting target configurationimmediately upon reception of the command but it shall apply/execute itonly if/when the associated condition is fulfilled. While the UEevaluates the condition it may continue operating per its currentserving cell RRC configuration, i.e., without applying the conditionalHO command.

When the UE determines that the condition is fulfilled, it disconnectsfrom the serving cell, applies the conditional HO command and connectsto the target cell. Once the UE applies the RRCConnectionReconfigurationincluding mobilityControlInfo, it shall not process any subsequentRRCConnectionReconfiguration messages received prior to the HOexecution.

However, before the HO condition is fulfilled, the UE may stay in thesource cell. During this period, the source cell should have means toperform further reconfigurations of the UE either to change the UEoperation in the current serving cell or to issue a (conditional orimmediate) handover to another target cell. In this scenario, thepreviously received conditional HO command cannot heretofore be appliedas a delta to the updated serving cell configuration (after applying theRRCConnectionReconfiguration) as the original conditional HO command wasbuilt as a delta to the previous RRC configuration, i.e., prior to thereception of the serving cell reconfiguration command.

The simplest solution would be that the UE discards the pendingconditional HO command when receiving a subsequentRRCConnectionReconfiguration from its source cell. But this implies thatthe source eNB must re-issue the conditional HO command towards the UE;now as a delta to the updated source cell configuration. However, as RRCconfiguration in the conditional HO command is built by the target eNB,this would imply additional inter-eNB signaling and subsequent Uusignaling.

One or more embodiments provide an efficient way to handle subsequentRRC reconfigurations as well as configurations towards multiple cellswhen using conditional HO solution.

Instead of simply discarding all pending (unfulfilled) conditional HOcommands upon reception of a subsequent RRCConnectionReconfiguration forthe current serving cell, the UE in some embodiments applies thesubsequent RRCConnectionReconfiguration for the serving cell as a deltato the current configuration of the serving cell; and it preserves thepreviously received pending conditional HO commands for the one or moretarget cells, i.e., the target cell configurations associated with thetarget cells are unaffected by the subsequentRRCConnectionReconfiguration for the serving cell.

Subsequent RRCConnectionReconfiguration

To avoid additional signalling between eNBs and towards the UE, the UEmay not discard the conditional HO command when receiving the subsequentRRCConnectionReconfiguration for the serving cell.

In accordance with a first example embodiment, upon reception of asubsequent RRCConnectionReconfiguration for the current serving cell,the UE applies the subsequent RRCConnectionReconfiguration for theserving cell as a delta to the current configuration of the servingcell; and it preserves the previously received pending conditional HOcommands for the one or more target cells, i.e., the target cellconfigurations associated with the one or more target cells areunaffected by the subsequent RRCConnectionReconfiguration for theserving cell.

In an example embodiment in accordance with the first exampleembodiment, when the UE receives either a conditional HO command or whenthe UE receives the subsequent RRCConnectionReconfiguration, the UEdetermines the target cell configuration from the current RRCconfiguration of the serving cell (before applying new receivedRRCConnectionReconfiguration) and from the delta configuration receivedin the conditional HO command; and the UE stores and preserves thedetermined target cell configuration.

An RRCConnectionReconfiguration for the source cell received after theconditional HO command for a target cell impacts therefore only theoperation towards the source cell but not the configuration towards thetarget cell.

In another example embodiment in accordance with the first exampleembodiment, the UE stores a received conditional HO command as well asthe current RRC context of the serving cell (assuming that theRRCConnectionReconfiguration is provided as a delta to the currentserving cell configuration). If the UE receives a subsequentRRCConnectionReconfiguration for the source cell, it applies thatreconfiguration but leaves the stored the current RRC context of theserving cell unaffected. When the trigger condition is fulfilled, the UEdetermines the target cell configuration from the stored serving cellconfiguration and delta received in the “conditional HO command” andthen uses that when HO is executed.

Updating a Conditional HO Command for a Target Cell

In another example embodiment, the network may decide to provide a new,updated RRCConnectionReconfiguration in a conditional HO command for atarget cell for which it had previously provided a conditional HOcommand. Correspondingly, if the UE receives a conditional HO commandfor a target cell for which it has already a pending conditional HOcommand, it determines the target cell configuration based on itscurrent serving cell configuration and the “delta” in the HO command anduses it to towards the target cell.

In another example embodiment, the network may indicate to the UE in theupdated conditional HO command, whether the contained configuration is adelta to the current serving cell configuration or to the previouslydetermined and preserved configuration of the target cell.Correspondingly, the UE either determines the new target cellconfiguration by applying the reconfiguration in the received updatedconditional HO command as a delta to its current serving cellconfiguration or as a delta to the previously determined configurationfor the target cell.

In another example embodiment, the network may only provide to the UE anupdated condition in a HO command for a cell for a target cell for whichit had previously provided a conditional HO command. If the UE receivessuch a conditional HO command with a new condition but without aRRCConnectionReconfiguration for a target cell for which it has alreadya pending conditional HO command, it preserves the previously receivedRRCConnectionReconfiguration but associates it with the received updatedcondition.

In an example embodiment according to any of the preceding exampleembodiments, the network may provide an updated configuration of apending conditional HO command. This may entail updating one of the setof allowed target cell beams or the random access configuration foraccessing the target cell.

Extending the Validity of a Conditional HO Command

The serving eNB operates the serving cell, which may be known as asource cell for a handover. The target eNB operates a neighbor celltowards which the UE is supposed to perform the handover. In this case,then, the neighbor cell may also be known as the target cell of thehandover. The serving eNB may ask the target eNB to prolong theconditional HO command validity and if granted by the target eNB, send anew time limit to the UE for the conditional HO command that extends thevalidity time, i.e., extends the time period during which the UE shouldevaluate the conditional HO command and during which it may trigger theHO if the condition is fulfilled.

If the UE receives such a conditional HO command with a new validitytime but without a RRCConnectionReconfiguration for a target cell forwhich it has already a pending conditional HO command, it may preservethe previously received RRCConnectionReconfiguration but associate itwith the received updated validity time.

Discarding Conditional HO Command

The source cell may at any time discard any outstanding conditional HOin the UE. If the UE receives such a command indicating that apreviously received conditional HO command for a target cell is nolonger valid, the UE may discard the previously receivedRRCConnectionReconfiguration and the associated condition. A UE may insome embodiments signal to the network that such cancellation issuccessful, implying that the stored related RRC state information hasbeen removed.

Replacing a Conditional HO Command for a First Target Cell by aConditional HO Command for a Second Target Cell

In another example embodiment, the eNB decides based on the RRMmeasurements that the potential target cell must be changed. In thisscenario, the source eNB provides the conditional HO command to the UEwith a new target cell and indicates that the UE shall discard theearlier provided conditional HO command. Correspondingly, the UE shallbe prepared to receive simultaneously the cancellation of a previouslyreceived pending HO command to a first target cell and a new/updatedconditional HO command for a second target cell. Such discard commandwould indicate to the UE to cancel a previously given HO command andremove all the stored related RRC state information. The command maytarget all the previously given conditional HOs, a given conditional HOor a specific target cell or a number of cells from a list of multiplecell sharing the same configuration given by theRRCConnectionReconfiguration. In this last case, the UE should keep thestored related RRC state information unless all the conditional HOcommand for cells sharing the same configuration are cancelled. A UE mayin some embodiments signal to the network that the new conditional HOcommand has been received and the cancellation of the indicatedconditional HO has been successful.

In FIG. 4 , inter-eNB signaling is presented for this scenario. Asshown, upon fulfillment of a measurement event (e.g., based on a low′threshold such as a thresholdY), the UE 40 sends a measurement report tothe serving gNB 50 (Step 1). The measurement report may include ameasurement quantity for a first target gNB 60-1. Based on the report,the serving gNB 50 in this example makes a decision to prepare the firsttarget gNB 60-1 for a potential handover (Step 1A). Based on thisdecision, then, the serving gNB 50 sends a handover request to the firsttarget gNB 60-1 (Step 2), which may happen earlier than in aconventional handover procedure given the low threshold for themeasurement report. Where the handover request is sent early in thisway, it may be referred to as an “early HO request” as shown in FIG. 4 .The first target gNB 60-1 accepts the handover in response to therequest, and builds an RRC configuration for the UE 40 to use with thefirst target gNB 60-1 (Step 2A). The first target gNB 60-1 then sends ahandover acknowledgement to the serving gNB 50 including the built RRCconfiguration (Step 3). The serving gNB 50 correspondingly sends aconditional handover command to the UE 40 that commands the UE 40 tohandover to the first target gNB 60-1 responsive to fulfillment of acondition (Step 4). This condition may be based on a ‘high’ threshold(E.g., thresholdX) that is higher than the low threshold which triggeredthe measurement report.

Before measurement of the first target gNB 60-1 fulfills the handovercondition (e.g., based on the high threshold), though, the UE 40 sendsanother measurement report to the serving gNB 50 (Step 5), including ameasurement quantity for a second target gNB 60-2. Based on the report,the serving gNB 50 in this example makes a decision to prepare thesecond target gNB 60-2 for a potential handover (Step 6). Based on thisdecision, then, the serving gNB 50 sends an early handover request tothe second target gNB 60-2 (Step 7). The second target gNB 60-2 acceptsthe handover in response to the request, and builds an RRC configurationfor the UE 40 to use with the second target gNB 60-2 (Step 8). Thesecond target gNB 60-2 then sends a handover acknowledgement to theserving gNB 50 including the built RRC configuration (Step 9). Theserving gNB 50 correspondingly sends a conditional handover command tothe UE 40 that commands the UE 40 to handover to the second target gNB60-2 responsive to fulfillment of a condition (Step 10). In thisexample, this latter conditional handover command operates to cancel thepending conditional handover to the first target gNB 60-1. The servinggNB 50 in some embodiments may then indicate to the first target gNB60-1 that the handover request is cancelled (step 11), e.g., so that thefirst target gNB 60-1 may release any resources it had reserved for thepotential handover.

Accordingly, this example demonstrates that based on RRM measurements,the serving eNB triggers HO negotiation towards gNB1. The serving cellsends the Conditional HO command to the UE in step 4. Later on, based onnew measurements, the serving gNB decides to trigger HO negotiationtowards target gNB2. The conditional HO command towards gNB2 as well asthe cancellation of the conditional HO command towards gNB1 is sent inStep 10 towards the UE. After that the serving eNB informs gNB1 thatearlier HO request is cancelled.

In one embodiment, the UE replies with a handover complete messagetowards the source eNB as a response to the conditional HO command RRCmessage. This confirms that the UE has successfully received theconditional HO command.

Multiple Cells Prepared

As explained above, it may be desirable to provide the UE with HOconditions and configurations for several candidate target cells. Whenreceiving conditional HO commands for multiple target cells, the UEevaluates HO conditions for more than one candidate target cell andstores configurations for those individually as described in theprevious subsection. However, this solution may lead to additionalcomplexity in the UE side especially because the UE may need to storeseveral configurations that have exactly the same resultingconfiguration in the target cell.

Therefore, in another example embodiment, the network informs in theconditional HO command that the RRCConnectionReconfiguration in theconditional HO command is applicable for several cells. That is to say,the same conditional HO command applies to multiple cells. When the UEreceives this kind of conditional HO command, it stores only oneconfiguration associated with multiple target cells.

In another example embodiment, the network provides a conditional HOcommand with multiple cells and potentially multiple configurations.When receiving such configuration, the UE stores the current servingcell RRC configuration (RRC context). When the HO is triggered, the UEderives the corresponding target cell configuration based on the sourcecell configuration stored upon reception of the HO command and theparameters provided in the conditional HO command.

Discarding Pending Conditional HO Commands Upon Handover

When the UE executes a handover to a target cell, that target cell sendsa path switch request to the core network (CN) upon which the CNforwards the newly arriving data to the target cell. Furthermore, the CNconfirms the path switch request towards the target and the targetinforms the source cell that it may release the UE context. In additionto that procedure the following is proposed.

In another example embodiment, the source cell should inform othertarget cells (if any) with which it had prepared a HO for the UE, thatthey may release their preparation for the inbound HO of the UE.

Similarly, the UE might have been configured with several conditional HOcommands. When the condition of one of these HO is fulfilled, the UEperforms the handover towards the target cell in accordance with theassociated RRCConnectionReconfiguration. According to one embodiment,the UE discards all other pending HO command (if any) upon executingmobility towards a target cell. This may be triggered due to fulfillmentof a conditional handover but also due a non-conditional handover. Andit may be a handover to a different cell or to the current serving cell(intra-cell HO).

While the early handover preparation is intended to increase the successof the HO execution, there may still be occasions where the UE triggersthe HO to a target cell but where the HO fails. In such cases, one mayconsider it premature that the UE discarded the conditional HO commandstowards other candidate target cells and the configuration for theprevious source cell. Hence, the following enhancement is proposed.

In another example embodiment, when executing a HO command the UEpreserves other pending conditional HO commands (if any) until havingsent the RRCConnectionReconfigurationComplete message to that targetcell (HO succeeded). If it does not receive the grant enabling it tosend the RRCConnectionReconfigurationComplete, it may continue toevaluate the conditions of the other pending conditional HO commands andexecute one of those when their condition is being fulfilled.

Generally, then, embodiments herein include a method in a terminaloperating in a wireless network. The method may be characterized byreceiving a conditional HO command, storing the current RRCconfiguration and the conditional HO command, selecting a target cellbased on a condition, deriving a target cell configuration from thestored RRC configuration and conditional HO command associated with theselected target cell, and sending Random Access andRRCConnectionReconfigurationComplete towards the target cell.

As discussed above, some embodiments allow efficient reconfigurations ofthe source cell configuration while the UE maintains and evaluates thepending conditional HO commands and the target cell configurationsassociated with those.

Note that embodiments herein are applicable to any type of wirelesscommunication system (e.g., Long Term Evolution, Wideband CDMA, GSM,Wifi or the like) for switching between links of any kind (e.g., cells,sectors, nodes, beams).

A network node herein is any type of node in the wireless communicationsystem 10, e.g., in the access network 12 or core network 14. A radionode herein is any type of node (e.g., a base station or wirelesscommunication device) capable of communicating with another node overradio signals. A radio network node is any type of radio node within theaccess network 12, such as a base station. A wireless communicationdevice or simply wireless device is any type of radio node capable ofcommunicating with a radio network node or another wirelesscommunication device over radio signals. A wireless communication devicemay therefore refer to a machine-to-machine (M2M) device, a machine-typecommunications (MTC) device, a narrowband internet of things (NB-IoT)device, etc. The wireless device may also be a user equipment (UE),however it should be noted that the UE does not necessarily have a“user” in the sense of an individual person owning and/or operating thedevice. A wireless device may also be referred to as a radio device, aradio communication device, a wireless terminal, or simply aterminal—unless the context indicates otherwise, the use of any of theseterms is intended to include device-to-device UEs or devices,machine-type devices or devices capable of machine-to-machinecommunication, sensors equipped with a wireless device, wireless-enabledtable computers, mobile terminals, smart phones, laptop-embeddedequipped (LEE), laptop-mounted equipment (LME), USB dongles, wirelesscustomer-premises equipment (CPE), etc. In the discussion herein, theterms machine-to-machine (M2M) device, machine-type communication (MTC)device, wireless sensor, and sensor may also be used. It should beunderstood that these devices may be UEs, but are generally configuredto transmit and/or receive data without direct human interaction.

In an IOT scenario, a wireless communication device as described hereinmay be, or may be comprised in, a machine or device that performsmonitoring or measurements, and transmits the results of such monitoringmeasurements to another device or a network. Particular examples of suchmachines are power meters, industrial machinery, or home or personalappliances, e.g. refrigerators, televisions, personal wearables such aswatches etc. In other scenarios, a wireless communication device asdescribed herein may be comprised in a vehicle and may performmonitoring and/or reporting of the vehicle's operational status or otherfunctions associated with the vehicle.

Note that a wireless device 16 as described above may perform the methodin FIG. 2 and any other processing herein by implementing any functionalmeans or units. In one embodiment, for example, the wireless device 16comprises respective circuits or circuitry configured to perform thesteps shown in FIG. 2 . The circuits or circuitry in this regard maycomprise circuits dedicated to performing certain functional processingand/or one or more microprocessors in conjunction with memory. Inembodiments that employ memory, which may comprise one or several typesof memory such as read-only memory (ROM), random-access memory, cachememory, flash memory devices, optical storage devices, etc., the memorystores program code that, when executed by the one or more processors,carries out the techniques described herein.

FIG. 5A for example illustrates the wireless device 16 in accordancewith one or more embodiments. As shown, the wireless device 16 includesprocessing circuitry 300 and communication circuitry (comm. circuitry)310. The communication circuitry 310 (e.g., in the form of atransmitter, receiver, transceiver, or radio frequency circuitry) isconfigured to transmit and/or receive information to and/or from one ormore other nodes, e.g., via any communication technology. Suchcommunication may occur via one or more antennas that are eitherinternal or external to the wireless device 16 as shown. The processingcircuitry 300 is configured to perform processing described above, e.g.,in FIG. 2 , such as by executing instructions stored in memory (MEM)320. The processing circuitry 300 in this regard may implement certainfunctional means, units, or modules.

FIG. 5B illustrates the wireless device 16 in accordance with one ormore other embodiments. As shown, wireless device 16 implements variousfunctional means, units, or modules, e.g., via the processing circuitry300 in FIG. 5A and/or via software code, for implementing thefunctionality described above (e.g., for implementing the steps in FIG.2 ). These functional means, units, or modules include for instance areceiving module or unit 340 for receiving the conditional switchcommand 22, a storing module or unit 350 for storing the information 30,and a performing module or unit 360 for performing one or moreoperations based on the stored information 30.

Also in view of the above modifications and variations, FIG. 6 generallyillustrates processing performed by a network node 16 according to someembodiments. As shown, the processing may include transmitting a command22 that commands a wireless communication device 16 to perform a linkswitch 24 from a source link 20A to a target link 20B responsive tofulfillment of a condition (Block 370). The command 22 may indicate atarget link configuration 26 relative to a source link configuration 28.Processing as shown in FIG. 6 may also include, after transmitting thecommand 22, changing the source link configuration 28 (Block 380).Moreover, processing may further include, after changing the source linkconfiguration 28, transmitting an updated command that indicates anupdated target link configuration relative to the source linkconfiguration before the source link configuration was changed (Block390).

In some embodiments, the method may also include signaling that theupdated command indicates the updated target link configuration relativeto the source link configuration before the source link configurationwas changed.

Also note that a network node 18 as described above may perform anyprocessing herein, by implementing any functional means or units. In oneembodiment, for example, the network node 18 comprises respectivecircuits or circuitry configured to perform the steps of processingdescribed herein (e.g., signaling). The circuits or circuitry in thisregard may comprise circuits dedicated to performing certain functionalprocessing and/or one or more microprocessors in conjunction withmemory. In embodiments that employ memory, which may comprise one orseveral types of memory such as read-only memory (ROM), random-accessmemory, cache memory, flash memory devices, optical storage devices,etc., the memory stores program code that, when executed by the one ormore processors, carries out the techniques described herein.

FIG. 7A illustrates the network node 18 in accordance with one or moreembodiments. As shown, the network node 18 includes processing circuitry400 and communication circuitry (comm. circuitry) 410. The communicationcircuitry 410 (e.g., in the form of a transmitter, receiver,transceiver, or radio frequency circuitry) is configured to transmitand/or receive information to and/or from one or more other nodes, e.g.,via any communication technology. Where the network node 18 is an accessnode (e.g., a base station), such communication may occur via one ormore antennas that are either internal or external to the network node18, as shown. The processing circuitry 400 is configured to performprocessing described above, such as by executing instructions stored inmemory (MEM) 420. The processing circuitry 400 in this regard mayimplement certain functional means, units, or modules.

FIG. 7B illustrates the network node 18 in accordance with one or moreother embodiments. As shown, the network node 18 implements variousfunctional means, units, or modules, e.g., via the processing circuitry400 in FIG. 7A and/or via software code. These functional means, units,or modules include for instance an signaling module or unit 440 forperforming signaling to/from the wireless device 16 as described above.

Those skilled in the art will also appreciate that embodiments hereinfurther include corresponding computer programs.

A computer program comprises instructions which, when executed on atleast one processor of a node (e.g., network node 18 or wireless device16), cause the node to carry out any of the respective processingdescribed above. A computer program in this regard may comprise one ormore code modules corresponding to the means or units described above.

Embodiments further include a carrier containing such a computerprogram. This carrier may comprise one of an electronic signal, opticalsignal, radio signal, or computer readable storage medium.

In this regard, embodiments herein also include a computer programproduct stored on a non-transitory computer readable (storage orrecording) medium and comprising instructions that, when executed by aprocessor of a node, cause the node to perform as described above.

Embodiments further include a computer program product comprisingprogram code portions for performing the steps of any of the embodimentsherein when the computer program product is executed by a computingdevice. This computer program product may be stored on a computerreadable recording medium.

The present invention may, of course, be carried out in other ways thanthose specifically set forth herein without departing from essentialcharacteristics of the invention. The present embodiments are to beconsidered in all respects as illustrative and not restrictive, and allchanges coming within the meaning and equivalency range of the appendedclaims are intended to be embraced therein.

What is claimed is:
 1. A method performed by a wireless communicationdevice configured for use in a wireless communication system, the methodcomprising: receiving, from an access node in the wireless communicationsystem, a command that commands the wireless communication device toperform a link switch from a source link to a target link responsive tofulfillment of a condition, wherein: the command indicates a relativetarget link configuration with respect to a source link configuration,the relative target link configuration comprising one or more parametervalues that are different between an absolute target link configurationand the source link configuration, and excludes one or more parametervalues that are the same between the target link configuration and thesource link configuration; and the command indicates the condition to befulfilled in order to perform the link switch; storing information, theinformation corresponding to the received target link configurationrelative to the source link configuration, wherein the storedinformation is associated with the condition such that the absolutetarget link configuration can be determined based on the storedinformation at the time the condition is fulfilled; and responsive tofulfillment of the condition, performing the link switch from the sourcelink to the target link using the target link configuration asdetermined from the stored information.
 2. The method of claim 1,wherein the command includes one or more changed parameter values thatare different between the target link configuration and the source linkconfiguration.
 3. The method of claim 2, wherein the stored informationcomprises information about a source link configuration in use at thetime the command is received and one or more of the changed parametervalues.
 4. The method of claim 3, further comprising determining thetarget link configuration from the stored information responsive to thefulfillment of the condition.
 5. The method of claim 3, furthercomprising determining the target link configuration responsive to arequest to change the source link configuration and updating the storedinformation to include the determined target link configurationinformation.
 6. The method of claim 3, further comprising, after thestoring information: changing the source link configuration; andpreserving the stored information irrespective of the change to thesource link configuration.
 7. The method of claim 2, further comprisingdetermining the target link configuration responsive to the command andstoring the target link configuration as the stored information.
 8. Themethod of claim 1, further comprising: receiving an update to thecondition, and updating the condition in accordance with the receivedupdate while preserving the stored information and the association ofthe condition with the stored information.
 9. A wireless communicationdevice configured for use in a wireless communication system, thewireless communication device comprising: communication circuitryconfigured for communication with network nodes in the wirelesscommunication system; and processing circuitry configured to: receive,from an access node in the wireless communication system, a command thatcommands the wireless communication device to perform a link switch froma source link to a target link responsive to fulfillment of a condition,wherein: the command indicates a relative target link configuration withrespect to a source link configuration, the relative target linkconfiguration comprising one or more parameter values that are differentbetween an absolute target link configuration and the source linkconfiguration, and excludes one or more parameter values that are thesame between the target link configuration and the source linkconfiguration; and the command indicates the condition to be fulfilledin order to perform the link switch; store information, the informationcorresponding to the received target link configuration relative to asource link configuration, wherein the stored information is associatedwith the condition such that the absolute target link configuration canbe determined based on the stored information at the time the conditionis fulfilled; and responsive to fulfillment of the condition, performthe link switch from the source link to the target link using the targetlink configuration as determined from the stored information.
 10. Thewireless communication device of claim 9, wherein the command includesone or more changed parameter values that are different between thetarget link configuration and the source link configuration.
 11. Thewireless communication device of claim 10, wherein the storedinformation comprises information about a source link configuration inuse at the time the command is received and one or more of the changedparameter values.
 12. The wireless communication device of claim 11,further comprising determining the target link configuration from thestored information responsive to the fulfillment of the condition. 13.The wireless communication device of claim 11, further comprisingdetermining the target link configuration responsive to a request tochange the source link configuration and updating the stored informationto include the determined target link configuration information.
 14. Thewireless communication device of claim 11, further comprising, after thestoring information: changing the source link configuration; andpreserving the stored information irrespective of the change to thesource link configuration.
 15. The wireless communication device ofclaim 10, further comprising determining the target link configurationresponsive to the command and storing the target link configuration asthe stored information.
 16. The wireless communication device of claim9, further comprising: receiving an update to the condition, andupdating the condition in accordance with the received update whilepreserving the stored information and the association of the conditionwith the stored information.
 17. The method of claim 1, wherein thesource link configuration is the source link configuration at the timethe conditional handover command is sent.
 18. The wireless communicationdevice of claim 9, wherein the source link configuration is the sourcelink configuration at the time the conditional handover command is sent.